High stability and low phase noise are achieved, as can be seen in the VCO output spectra shown below. leaving 50 bps data modulation. Introduction: This is a premium GPS signal repeater set to solve indoor GPS signal receiving problems. Its responses are collected by the host from the bridge on the next scan. An iterative method is used because the equations are non-linear. Pi software development was done "head-less" via SSH and FTP over a USB Wi-Fi dongle. and ensures low overall system noise figure, even if long antenna cables are used. NAV data transmitted by the satellites is collected in FPGA memory. The first local oscillator was changed to 1552.82 MHz, moving the first and second IF frequencies to 22.6 MHz and 2.6 MHz respectively. Calculating peak to average power over this data gives a good estimate of SNR and is used to find the strongest signals. FORTH is a stack-based language, which basically means the CPU has stacks instead of general purpose registers. FORTH is not mainstream; and its use here might be an esoteric barrier; It still amazes me how well frequency domain information is preserved through hard-limiting! L4, L5 and L6 are screened Toko 7mm coils. I and Q complex baseband products from the second rank of XOR gate mixers are summed over 10000 samples or 1ms. Each channel having to wait its turn, NCO rate-updates can be delayed by tens or hundreds of microseconds after a code epoch; but this introduces negligible phase shift at frequencies where phase margin is determined. Transmissions can be done via two radios directly on the same frequency, called simplex, or they can use a transmitter in between, called a repeater. however, this is not essential if a fast FFT-based search is used. Ephemerides are regularly updated and satellites only transmit their own. Connectivity to a standard GPS antenna is done through a powered (3V3) SMA connector. 64-bit precision is used and gain coefficients KI and KP, although restricted to powers of 2, are dynamically adjustable. Thermal noise power in the same bandwidth is -111 dBm, so a GPS signal at the receiving antenna is ~ 20 dB below the noise floor. Code length is 1023 chips and chip rate is 1.023 Mbps. Near left is a temperature-compensated voltage-controlled crystal oscillator (TCVCXO) providing a stable reference frequency, vital for GPS reception. Built-in GPS receiver with 1-Pulse Per Second (1PPS) giving you a stratum-1 time source capability, the most accurate time source you can get for ensuring your controllers clock never drifts. Other source files include: There is no Arduino in this project, but its LCD driver files LiquidCrystal.cpp and LiquidCrystal.h are used. Fortunately, code Doppler is proportional to carrier Doppler for which we have a good estimate. The code repeats 20 times per data bit. Parity errors do not occur unless samples stray into the opposite half of the IQ plane. Source code and documentation can be found towards the bottom of this page. A small notch due to BPSK carrier suppression can just be seen: These spectra show the same de-spread transmission at different spans and resolution bandwidths (RBW). as a dedicated frequency synthesizer, The official US government GPS Interface Specification [3] is an essential reference. Extend Parrot Drone Range – Mainboard / Antennae Mod Or WiFi Repeater. Follow these easy steps, and then check out the video if you need extra clarification. HC-12 transceiver paired with an Adafruit GPS shield . © 1996-2020 Ziff Davis, LLC. Fortunately, DSSS receivers are tolerant of narrow-band interferers, external or self-generated. The TCVCXO is good; but not quite up to GPS standard when operating un-boxed in windy locations. When Frac5 was originally developed, Weak GPS signals only influence the comparator near zero crossings! A service request flag signals the CPU, which reads the data bit-serially. I was effectively ignoring Earth's rotation during the 60 to 80 ms that signals were in flight. This fragment gives some flavour of source style. L1 frequencies are down-converted to a 1st IF of 22.6 MHz by mixing with a 1552.82 MHz local oscillator on the "GPS3" front-end board. After booting from SD-Card, the GPS application software starts automatically. Three fully-differential IF amplifier stages follow the mixer. but also hosts a fractional-N frequency synthesizer. Doppler shift on the 1575.42 MHz carrier is ±5 KHz or ±3 ppm. Download the zip file and extract it into a folder where you can see a firmware folder that has three bin files (which will be used in later stages). Typical CCF output is illustrated below: of Matjaž Vidmar, S53MV, who developed a GPS receiver from scratch, using mainly discrete components, over 20 years ago. You … Thus downloaded, binary images execute automatically. First – a GPS Repeater System is a device that relays GPS signals to any indoor location that isn’t normally reachable. A short run of coax connects the two as previously noted. Noise power in such bandwidths is small and the loops can track very weak signals. At 10 MHz sampling rate, code phase is resolved to the nearest 100ns. Its 1-bit ADC is the 6-pin IC near the pin headers, an LVDS-output comparator. FalTech GPS is a company specialised in GPS repeater technology, providing indoor coverage solutions that allow GPS-enabled devices to be used, tested, repaired and calibrated inside any building or space where it was previously impossible. That any of the signals present, superimposed one on another and buried in noise, It is the ideal device for boost mobile phone signal. but accuracy is typically ±5 metres in poorer locations with fewer satellites. They run about $1500. Grid squares are 0.001° on each side. 24 instructions out of a possible 32 are currently allocated in the opcode space h80XX - h9FXX. and only 50% of the FPGA fabric is required for an 8-channel receiver or 67% for 12-channels. It can receive outdoor GPS satellite signal, through wave filtration, amplification, transfer etc. The device is also slightly sensitive to infra-red e.g. Code phase is tracked using a conventional delay-locked loop or "early-late" gate. This low-pass filtering dramatically reduces noise bandwidth and thereby raises SNR. I wrote a simulation to convince myself. For bi-level signals, the mixers are simple XOR gates. however, this same characteristic makes them poor at acquiring lock without help. This diagram helps to get the error sense correct: A Costas Loop is used for carrier tracking and NAV data recovery in the punctual channel. A repeater offers an easier, more convenient, less time-consuming way to work with a wide range of GPS-enabled systems, but what does a GPS repeater system consist of? But that first version was not portable: it had inconvenient power requirements and no on-board frequency standard. Now…building your own GPS receiver is as “simple” as receiving and demultiplexing four GPS signals — but don’t let the image above fool you: there is a Xilinx FPGA dev board that performs real-time signal processing that isn’t pictured, and a Windows PC has a supervisory role, picking out healthy satellites, analyzing the data received, and so on. Memory accesses can be 16-, 32- or 64-bits, word-aligned. The above kI and kP work for most signals, but need dropping one notch for the very strongest. Amplified thermal noise must comfortably exceed this to keep it toggling. here's an article on how to hack your Linksys router to act as a repeater. Initial phases and frequencies must be preset to the measured code phase and Doppler shift of the target satellite. Below is a Bode plot of open-loop gain for the Costas Loop at k=500: Costas Loop bandwidth is around 20 Hz, which is about optimal for carrier tracking. Hidden under noise but not obliterated in the bi-level quantised mush that emerges are signals from every satellite in view. Visitors to my Mark 1 FORTH Computer page will already be aware of my interest in the language. Here, we see this available power spread across a range of frequencies. In that original version, four identical instances of the "tracker" module filled the FPGA. ½ chip ahead-of and behind punctual. 2.6 MHz lies close to the centre of the 5 MHz Nyquist bandwidth. R9 terminates the IF port. Doppler shift was -1.2 KHz. Repeater Operation - Operating using a repeater isn't difficult. One might expect jitter problems, co-hosting a phase detector with other logic, but it works. Currently, the Pi is running Raspbian Linux. I've created an appendix showing how the iterative solution is developed, The loops should be in-lock from the outset and remain so. All GPS satellites transmit on the same frequency, 1575.42 MHz, using direct sequence spread spectrum (DSSS). Finally, just to add a soupçon of illicit naughtiness: every commercial GPS device must be restricted from working at altitudes above 60,000 feet and at speeds over 1,000 knots — to prevent you from building your own intercontinental ballistic missiles, which is actually the primary purpose of the US Department of Defence-created GPS. Mixing with the same code in the correct phase de-spreads the wanted signal and further spreads everything else. 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